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Part of Te map from Figure 2 with geological features and aeromagnetic lineaments. DML, Dronning Maud Land; GC, Grunehogna craton; GSM, Gamburtsev Subglacial Mountains; GM, Grove Mountains; HF, Heimefront shear zone; NPC, Northern Prince Charles Mountains; LG, Lambert Graben; RC, Ruker Craton; SPC, Southern Prince Charles Mountains; SR, Sør Rondane; WOF, western orogenic front of EAAO (Reidel et al., 2013); K, Kohnen lineament & FMA, Forster magnetic anomaly (Mieth & Jokat, 2014); a, b, c (from Ruppel et al., 2018); GS, Gamburtsev Suture (Ferraccioli et al., 2011); TOAST (Tonian Oceanic Arc Superterrane; Jacobs et al., 2015); VCC, Valkyrie cryptic Craton (Jacobs et al., 2020); thin white lines are the East Antarctic Rift System.
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East Antarctica is the least well‐exposed Precambrian shield on Earth. What is known, or surmised, of its geological structure comes from extrapolation over large distances and from geophysics. Here, we present a map of effective elastic thickness, Te, computed from Antarctic bedrock topography and both terrestrial and satellite gravity data. Te is...
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The landscape of Antarctica, hidden beneath kilometre‐thick ice in most places, has been shaped by the interactions between tectonic and erosional processes. The flow dynamics of the thick ice cover deepened pre‐formed topographic depressions by glacial erosion, but also preserved the subglacial landscapes in regions with moderate to slow ice flow....
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... Low values of |k 0 | provide better spatial resolution, while large values give a good resolution in the wave-number domain and a reasonably good resolution in the space domain. In this way, the results with different |k 0 | can be interpreted as the result of applying different band-pass filters to T e , bearing in mind that absolute T e values are more reliable for higher |k 0 | wavelets, while relative T e differences are more faithfully represented by lower |k 0 | wavelets (Kirby & Swain, 2011;Swain & Kirby, 2021). All of this can be seen in Figure 4, where the obtained T e map with the |k 0 | = 2.668 shows a more detailed T e structure, whereas T e results from |k 0 | = 5.336 show a spatially smoother T e pattern within the region. ...
The Eastern Central Atlantic (ECA) region includes the Azores, Canary, Cape Verde, Great Meteor, and Madeira hotspots. These hotspots exhibit a large variety of characteristics and are rooted in the lithosphere ranging in age from newly created at the Mid Atlantic Ridge to Jurassic at the NW Africa Atlantic margin. Therefore, the ECA region represents an excellent scenario to investigate in an integrated way the effects of hotspots on the mechanical structure of oceanic lithosphere. Here, we calculate the effective elastic thickness (Te) of the lithosphere from an analysis of gravity and topography. Azores hotspot is characterized by a Te < 10 km, whereas the Great Meteor, Cape Verde, and Madeira hotspots have intermediate Te (15–30 km) values. In contrast, the Canary hotspot is characterized by a much higher Te (>50 km), forming the largest and most prominent mechanical feature in the ECA. All the hotspots except Canary show standard elastic thickness values when compared to average values for the same age lithosphere and to other oceanic areas in the world. The high strength of the Canary hotspot may be related to the highly depleted mantle composition in the area. The comparison between the elastic thickness distribution and the upper mantle seismic velocity structure shows no correlation between the Te estimated at the ECA hotspots (with the exception of Azores) and the presence of low shear‐wave velocity anomalies in the underlying mantle. This lack of correlation suggests a negligible effect of upper mantle temperature anomalies on the flexure of the ECA region.
... In the East Antarctic highlands, including the Gamburtsev Subglacial Mountains, Vostok Subglacial Highlands and coast-parallel mountains in Dronning Maud Land, Figure 9b illustrates that the differences between the predicted and inverted Moho depths are within ±5 km; this suggests that the crust is largely compensated in these areas and agrees with previous findings by . The low lithospheric strength beneath these areas (Chen et al., 2017;Paxman et al., 2016;Swain & Kirby, 2021) also indicates that the high elevation is supported isostatically by the observed thickened crust (Figure 7). Moreover, a marked negative anomaly (Figure 9b) is present in the seaward area of coast-parallel mountains in Dronning Maud Land, where a great escarpment has developed with elevations decreasing from 3 km to hundreds of meters, suggesting that they are isostatically overcompensated. ...
... Therefore, we attribute the negative isostatic anomalies along this escarpment to the deeper observed Moho than that isostatically estimated using the present eroded topography (Eagles et al., 2018). The large Moho depth beneath the great escarpment in Dronning Maud Land is controlled by its strong lithosphere (Swain & Kirby, 2021) that has prevented the Moho from being isostatically adjusted upward after unloading due to glacial erosion occurred, resulting in a modern overcompensated isostatic state. This explanation is also suitable for the broad negative anomalies in the areas from the Aurora Subglacial Basin to the Wilkes Subglacial Basin (∼100°-160°E) (Figure 9b), where glacial erosion (∼1 km) and relatively high (Chen et al., 2017;Ji et al., 2017;Swain & Kirby, 2021) has produced insufficient elevation uplift of 200-300 m (Paxman et al., 2019), far from Airy isostasy. ...
... The large Moho depth beneath the great escarpment in Dronning Maud Land is controlled by its strong lithosphere (Swain & Kirby, 2021) that has prevented the Moho from being isostatically adjusted upward after unloading due to glacial erosion occurred, resulting in a modern overcompensated isostatic state. This explanation is also suitable for the broad negative anomalies in the areas from the Aurora Subglacial Basin to the Wilkes Subglacial Basin (∼100°-160°E) (Figure 9b), where glacial erosion (∼1 km) and relatively high (Chen et al., 2017;Ji et al., 2017;Swain & Kirby, 2021) has produced insufficient elevation uplift of 200-300 m (Paxman et al., 2019), far from Airy isostasy. ...
The information on crustal thickness in Antarctica can provide significant constraints on its crustal deformation and tectonic evolution. To generate reliable images of crustal features, we investigate the model of Moho depth and crustal thickness beneath Antarctica by applying the Bott‐Parker's formulas based on the Gauss‐fast Fourier transform method through a comprehensive analysis of gravity data, ice and sediment thicknesses and bedrock elevation, combined with seismic constraints. Tests with synthetic data indicate that the iterative inversion algorithm can yield a highly accurate Moho topography. Ultimately, inverted crustal thickness reveals a more detailed crustal image by clearly identifying more tectonic elements at different scales than previous results and correlates well with major tectonic provinces. Airy isostasy and flexural isostasy models are used to assess the crustal isostatic compensation. The distinctive negative isostatic anomalies are observed in the Transantarctic Mountains and the East Antarctic areas of the great escarpment in the Dronning Maud Land and Aurora and Wilkes Subglacial Basin, indicating that the low density of the uppermost mantle and lithospheric strength may play important roles in compensating for their elevations. Variations in crustal thickness in interior East Antarctica are analyzed; the thickened crust from Dronning Maud Land to the Gamburtsev Subglacial Mountains may be associated with the collision of continental blocks and is interpreted as the fossil sutures. We compare the relationship between the Moho and Curie interfaces and find that the uppermost mantle is magnetized in some areas of East Antarctica, which may indicate preserved Precambrian cratonic roots.
... Reliable estimates of T e have historically been difficult to establish in the polar regions, given the sparse coverage of geological and geophysical observations and poorly constrained crustal structure. However, we used laterally variable T e grids that have recently been derived using continental-scale spectral analysis of gravity and topography data in Antarctica 17 and Greenland 16 (Fig. 1e,f). ...
The land surface beneath the Greenland and Antarctic Ice Sheets is isostatically suppressed by the mass of the overlying ice. Accurate computation of the land elevation in the absence of ice is important when considering, for example, regional geodynamics, geomorphology, and ice sheet behaviour. Here, we use contemporary compilations of ice thickness and lithospheric effective elastic thickness to calculate the fully re-equilibrated isostatic response of the solid Earth to the complete removal of the Greenland and Antarctic Ice Sheets. We use an elastic plate flexure model to compute the isostatic response to the unloading of the modern ice sheet loads, and a self-gravitating viscoelastic Earth model to make an adjustment for the remaining isostatic disequilibrium driven by ice mass loss since the Last Glacial Maximum. Feedbacks arising from water loading in areas situated below sea level after ice sheet removal are also taken into account. In addition, we quantify the uncertainties in the total isostatic response associated with a range of elastic and viscoelastic Earth properties. We find that the maximum change in bed elevation following full re-equilibration occurs over the centre of the landmasses and is +783 m in Greenland and +936 m in Antarctica. By contrast, areas around the ice margins experience up to 123 m of lowering due to a combination of sea level rise, peripheral bulge collapse, and water loading. The computed isostatic response fields are openly accessible and have a number of applications for studying regional geodynamics, landscape evolution, cryosphere dynamics, and relative sea level change.
The Antarctic ice sheet blankets >99% of the continent and limits our ability to study how subglacial geology and topography have evolved through time. Ice-rafted dropstones derived from the Antarctic subglacial continental interior at different times during the late Cenozoic provide valuable thermal history proxies to understand this geologic history. We applied multiple thermochronometers covering a range of closure temperatures (60–800 °C) to 10 dropstones collected during Integrated Ocean Drilling Program (IODP) Expedition 318 in order to explore the subglacial geology and thermal and exhumation history of the Wilkes Subglacial Basin. The Wilkes Subglacial Basin is a key target for study because ice-sheet models show it was an area of ice-sheet retreat that significantly contributed to sea-level rise during past warm periods. Depositional ages of dropstones range from early Oligocene to late Pleistocene and have zircon U-Pb or 40Ar/39Ar ages indicating sources from the Mertz shear zone, Adélie craton, Ferrar large igneous province, and Millen schist belt. Dropstones from the Mertz shear zone and Adélie craton experienced three cooling periods (1700–1500 Ma; 500–280 Ma; 34–0 Ma) and two periods of extremely slow cooling rates (1500–500 Ma; 280–34 Ma). Low-temperature thermochronometers from seven of the dropstones record cooling during the Paleozoic, potentially recording the Ross or Pan-African orogenies, and during the Mesozoic, potentially recording late Paleozoic to Mesozoic rifting. These dropstones then resided within ~500 m of the surface since the late Paleozoic and early Mesozoic. In contrast, two dropstones deposited during the mid-Pliocene, one from the Mertz shear zone and one from Adélie craton, show evidence for localized post-Eocene glacial erosion of ≥2 km.
The subglacial landscape of Antarctica records and influences the behaviour of its overlying ice sheet. However, in many places, the evolution of the landscape and its control on ice sheet behaviour has not been investigated in detail. Using recently released radio-echo sounding data, we investigate the subglacial landscape of the Evans-Rutford region of West Antarctica. Following quantitative analysis of the landscape morphology under ice-loaded and unloaded conditions, we identify ten flat surfaces distributed across the region. Across these ten surfaces, we identify two distinct populations based on clustering of elevations, which potentially represent remnants of regionally coherent pre-glacial surfaces underlying the West Antarctic Ice Sheet (WAIS). The surfaces are bounded by deeply incised glacial troughs, some of which have potential tectonic controls. We assess two hypotheses for the evolution of the regional landscape: (1) passive margin evolution associated with the breakup of the Gondwana supercontinent, or (2) an extensive planation surface that may have been uplifted either in association with the West Antarctic Rift System or cessation of subduction at the base of the Antarctic Peninsula. We suggest that passive margin evolution is most likely of these two mechanisms, with the erosion of glacial troughs adjacent to, and incising, the flat surfaces likely having coincided with the growth of the WAIS. These flat surfaces also demonstrate similarities to other identified surfaces, indicating that a similar formational process may have been acting more widely around the Weddell Sea Embayment. The subsequent fluctuations of ice flow, basal thermal regime and erosion patterns of the WAIS are therefore controlled by the regional tectonic structures.
The East Antarctic Ice Sheet (EAIS) has its origins ca. 34 million years ago. Since then, the impact of climate change and past fluctuations in the EAIS margin has been reflected in periods of extensive vs. restricted ice cover and the modification of much of the Antarctic landscape. Resolving processes of landscape evolution is therefore critical for establishing ice sheet history, but it is rare to find unmodified landscapes that record past ice conditions. Here, we discover an extensive relic pre-glacial landscape preserved beneath the central EAIS despite millions of years of ice cover. The landscape was formed by rivers prior to ice sheet build-up but later modified by local glaciation before being dissected by outlet glaciers at the margin of a restricted ice sheet. Preservation of the relic surfaces indicates an absence of significant warm-based ice throughout their history, suggesting any transitions between restricted and expanded ice were rapid.
In this study, we explore the impact of using different Moho surfaces on the reconstruction of the upper mantle geophysical parameters. The study area is the subsurface of the Antarctica continent. Using the optimization program of Sequential Integrated Inversion (SII) and the gravity anomalies synthetized by a global Gravity Field Model (GFM), we reconstructed the upper mantle density and the related 3D distribution of the rho-vsv couplings down to the depth of 400 km, with a lateral resolution of 0.5° × 0.5°. Here, we present the results obtained for four models, built with four different Moho surfaces. A correlation analysis showed that different Moho structures affect the optimization of the intensity of the anomalies and the rho-vsv couplings. The possibility of having both a density model and a 3D distribution of the- couplings enables us to highlight several significant features for all models that are not disclosed by seismic tomography. Among them, a trend of positive, presumably compositional anomalies suggests the contribution of the Lambert Rift System (LRS) to the Gamburstev Mountains (GSM) uplift, which in turn may have influenced the formation of the Maud Subglacial Basin (MSB). A continuous low-density anomaly and positive rho-vsv phase coupling anomaly, extending from the northwestern side of the Transantarctic Mountains (TAM) to Victoria Land, support the thermal buoyancy force as the causative element of the formation of the TAM. A circumscribed negative density anomaly extending up to depth of 365 km, which is associated to a negative variation in the angular coefficients of the rho-vsv couplings, indicates the presence of an active magmatic system in the upper mantle or a Cenozoic mantle plume beneath the region of Mary Byrd Land (MBL).
